1. Field of the Invention
This invention generally relates to card cages and other housings for supporting printed circuit boards in electronic equipment and more specifically to front panels useful in the insertion and extraction of printed circuit boards from such card cages and housings.
2. Description of Related Art
Card cages are a form of housing for supporting printed circuit boards in compact or dense configurations. They generally comprise an open framework with a top, bottom, back and sides. Front support rails define an open front through which the printed circuit boards are inserted into the card cage. The back typically supports a backplane with backplane connectors for receiving mating connectors on a rear edge of each printed circuit board. Rails attached to the top and bottom or to the sides or intermediate locations generally engage parallel edges of the printed circuit board (i) to guide the printed circuit board into the card cage in either a vertical or horizontal orientation, (ii) to align the printed circuit board connector with a corresponding backplane connector and (iii) to support the printed circuit board after it is seated in the card cage.
Oftentimes it is desirable to lock the printed circuit board in place. In some situations apparatus as simple as a machine screw that leads through a lead hole in a front panel and threads into a front support rail provides this locking function. In other situations it is desirable to provide a ready means for removing or extracting a printed circuit board from the card cage for maintenance, upgrade or other purposes and for then reinserting the same or another printed circuit board into the card cage. Diverse front panel and other structures have evolved for facilitating such insertion and extraction operations. For example, in U.S. Pat. Nos. 4,525,771 and 5,216,529 specially formed structures and card cages position printed circuit boards in the card cages.
U.S. Pat. No. 4,525,771 of Hanseler et al. discloses a modular assembly in the form of a card cage with guide rails that receive parallel edges of a printed circuit board. Each printed circuit board has a front panel. Nose members at the ends of each front panel fit into grooves formed in the leading edges of top and bottom transverse rails. A latching device at the rear edge of each printed circuit board engages a metal strip at the backplane. A rail-like securing member provides elastic shock absorbing fastening. This securing member overlies all the front panels and attaches to the side walls of the card cage. Transverse shock absorbing profiled sectional members between the side walls lock the front panels in place.
U.S. Pat. No. 5,216,578 to Zenitani et al. discloses a printed circuit board holding structure with a pair of linear guide members that attach to the edges of the printed circuit board and a pair of support members for receiving the respective guide members. The support members cantilever from a backplane and carry backplane connectors that receive mating printed circuit board connectors. The housing has positioning apertures to be fitted to contact pins projected from the backplane.
U.S. Pat. Nos. 4,648,009; 4,947,289; 4,996,631 and 5,140,501 depict other front panel embodiments. These front panels are adapted for inserting and extracting printed circuit boards from standard card cages.
U.S. Pat. No. 4,648,009 to Beun et al. discloses an articulated latch for use with the printed circuit board. The latch comprises an actuating member pivotally secured to a latching member. The latching member attaches to a base plate on a printed circuit board. The actuating and latching members have an interface mechanism comprising a cooperating tab, slots and wells for allowing the actuating member to lock to the latching member in at least two positions. The actuating member stores in approximately a horizontal position when the printed circuit board is fully inserted in a card cage.
U.S. Pat. No. 4,947,289 to Dynie discloses a latch mechanism for a plug-in cartridge that comprises a body portion, a pair of walls extending from the body portion, a camming portion and an actuating portion. The walls have apertures that are snap locatable into detents on a specially constructed face plate thereby resiliently latching the latching mechanism when a printed circuit board is fully inserted into a cabinet. The camming portion projects from the latching mechanism and cooperates with the actuating portion to function as a lever, the camming portion being engageable with an inside surface of a mating apparatus to establish a first engagement about which the latching mechanism is levered to overcome an insertion force. The camming portion also can engage an outside surface of the mating apparatus to establish a second engagement about which the latching mechanism is levered to overcome an extraction force. When the latching mechanism is in a latched position, it is flush with a face plate. Extraction requires the actuating portion to be levered out from the face plate by a blade or the like.
U.S. Pat. No. 4,996,631 to Freehauf discloses a circuit board injector-ejector system with a lever handle that mounts for rotation on an exterior corner of the circuit board. The lever handle extends out and through an opening formed in a front panel. Selective rotation of the lever handle inserts or extracts the circuit board with only one of a pair of finger extensions located on the lever arm being cooperatively engaged with the printed circuit board, depending upon the direction of lever handle rotation.
U.S. Pat. No. 5,140,501 to Takahashi et al. discloses a mechanism for inserting and withdrawing a printed circuit board from a card cage. A lockarm with a flexible tip and a base portion attaches to the printed circuit board. A lever pivots on the printed circuit board and has a cam surface that drives the lock arm for inserting and extracting of the printed circuit board into and from the card cage. An aperture formed at the bottom of the card cage engages the lock arm when the printed circuit board is fully inserted. The lever thereby indicates, by its angular position, whether the printed circuit board is inserted fully.
Other front panel embodiments have also become commercially available for positioning printed circuit boards in card cages. For example, Electronics Solutions, of San Diego, Calif. provides a front panel with brackets that mount the front panel to the printed circuit board. A handle having a cam portion extends through a slot in the front panel and pivots on the printed circuit board. The cam portion is intermediate the pivot point and the handle so it can bear against a support rail and partially eject an attached printed circuit board from the backplane connector.
Schorff, Incorporated, of Warwick, R.I. provides a similar front panel that includes a central panel portion, upper and lower hinges, and handles for connection to the hinges. The front panel attaches to the hinges that in turn, bolt to printed circuit board. Each handle provides a double camming surface that straddles the hinge and apparently is held in place by a standard pin. Each hinge also carries a screw for mounting the hinge to the card cage. In this particular embodiment, the handle has a finger pad or flat surface that extends at right angles to the panel and not parallel to the panel, as is the industry preference. It also appears that as the circuit board is inserted, the lower handle can assume an orientation that can block the insertion process.
As each of these and other front panels have been developed, a series of desirable features and characteristics have evolved. For example, during extraction, the front panel should completely disengage the backplane and printed circuit board connectors. The ejection mechanism should not overlap any significant portions of the printed circuit board. The forces required to eject the board should transfer to the printed circuit board evenly and the printed circuit board should move in its plane without bending. The front panel should be rugged and reliable in use and should be readily adapted for use as connectors with a variety of printed circuit boards at different locations. The operative handle should reliably hold labels. Moreover, the label surface should parallel the front panel plane when the printed circuit board is fully inserted in the card cage. The label surfaces on adjacent front panels should remain aligned to facilitate identification and provide a pleasing appearance. In addition these assemblies should reduce inventory requirements and be manufactured at minimal cost.
None of the prior art front panels satisfy all of these requirements. For example, the commercially available panel structures generally have injection molded plastic handles. Some handles provide no structure for a label. Generally they all wear with use and are subject to misalignment. In many of these assemblies the forces required to remove the printed circuit board are not transferred uniformly to the printed circuit board, particularly front panels using a single cam. In other panels, as shown in the foregoing patents, the insertion/ejection operation may overlap large portions of the printed circuit board and limit the area available for circuitry. Some panels require external tools. Others require overly complicated manipulation during the insertion or extraction process.